In the field of composite fabric manufacturing, it is known to obtain so-called “3D products” by using different materials for the warp and weft yarns of a fabric. For instance, in the field of aircraft and automotive industry, there is a need to manufacture composite structures with a form close to their final form, in order to save expensive material, such as carbon, and in order to avoid weaving large quantities of material which will be later removed from the final fabric and thrown away.
Usually, manufacturers define the portions of a fabric where a tridimensional pattern is to be created. Then, they draw reinforced weft yarns in these portions which are later cut to fit the shape of the final product. The parts of the product which are cut away are wasted and may include a significant quantity of expensive material including, for instance, reinforced fibers made of carbon, Kevlar (registered trademark), glass, etc. Once the fabric has been cut to fit its final shape, it is usually installed within a mold where it is thermoset with added resin.
In classical looms, weft yarns are drawn into the open shed and extend all through the width the fabric. Such known looms are not flexible, because weft yarns are inserted with a fixed length in the whole fabric.
In order to save some material, WO-A-2013/104056 teaches to weave blanks of reinforcement fibers. The full fabric contains reinforced warp threads and a part of these threads is later cut away, so that material waste is not fully avoided.
EP-A-2 531 639 explains how to add weft effects in order to obtain a pattern on a fabric. The added weft thread is endless and the technology required for implementing this method is based on needles, which is complicated.
EP-A-2 832 906 discloses a method for weaving a fabric with short length weft threads and non-woven side parts, which must be cut away. The short weft yarns are likely to be imprecisely positioned with respect to the warp yarns if a high speed loom is used.
On the other hand, it is known from FR-A-2 902 444 to use electrical actuators in order to drive heddles of a weaving loom and to adapt the shed, depending on parameters provided by the weaver. Weft yarns are supposed to extend all through the width of the fabric.